The present invention relates generally to antennas and more particularly to a broader bandwidth isotropic planar inverted F antenna.
Planar inverted F antennas (PIFAs) are used in wireless communications, e.g., cellular telephones, wireless personal digital assistants (PDAs), wireless local area networks (LANs)—Bluetooth, etc. The PIFA generally includes a planar radiating element having a first area, and a ground plane having a second area that is parallel to the radiating element first area. An electrically conductive first line is coupled to the radiating element at a first contact located at an edge on a side of the radiating element. The first line is also coupled to the ground plane. An electrically conductive second line is coupled to the radiating element along the same side as the first line, but at a different contact location on the edge than the first line. The first and second lines are adapted to couple to a desired impedance, e.g., 50 ohms, at frequencies of operation of the PIFA. In the PIFA, the first and second lines are perpendicular to the edge of the radiating element to which they are coupled, thereby forming an inverted F shape (thus the descriptive name of planar inverted F antenna).
The resonance frequency of the PIFA is determined, generally, by the area of the radiating element and to a lesser extent the distance between the radiating element and the ground plane (thickness of the PIFA assembly). The bandwidth of the PIFA is generally determined by thickness of the PIFA assembly and the electrical coupling between the radiating element and the ground plane. A significant problem in designing a practical PIFA application is the trade off between obtaining a desired operating bandwidth and reducing the PIFA volume (area×thickness). Furthermore, it is preferably that a larger ground plane area (shield) helps in reducing radio frequency energy that may enter into a user's head (SAR value=specific absorption rate), e.g., from a mobile cellular telephone. However, the volume of the PIFA increases with a larger ground plane area unless the thickness (distance between the radiating element and ground plane areas) is reduced.
As the number of wireless communications applications increase and the physical size of wireless devices decrease, antennas for these applications and devices are needed. Prior known planar inverted F antennas have sacrificed bandwidth by requiring a reduction in the volume (thickness) of the PIFA for a given wireless application.
Therefore, there is a need for improving the bandwidth of a PIFA without having to increase the volume (thickness) thereof.